This invention relates to a video processing system to allow a video image to be stored in a frame store at a selected rotational angle.
In television broadcasting for example there is often a requirement to rotate a video image for use in special effects. It has been should in U.K. patent application No. 8108467 (U.S. patent application Ser. No. 246,970) that this can be achieved by storing the video signal frame by frame in a digital frame buffer and then reading out each frame using a modified addressing mechanism such that the resultant image is a rotated form of the original.
FIG. 1 shows an example of the addressing mechanism used in the above referenced patent application that is required to produce this rotated image (O/P raster). In this example in order to calculate the new address B from the previous address A we add on two incremental steps dX and dY where for no compression dX=1.times.Cos O and dY=1.times.Sine O where O is the angle of rotation.
If the position of pixel A when projected onto the framestore raster is X,Y then the position of B will be X+dX, Y+dY. This co-ordinate position is non-integer and so we can calculate the surrounding picture points, P, Q, R and S which we need to calculate the new pixel value for the position B by taking the integer part of B's co-ordinate. The remainder (or fractional part) dX and dY is used to calculate the relative weightings of the pixel values at P, Q, R and S in order to provide a correctly interpolated pixel value of the position B.
In the example shown in FIG. 1, point B to be synthesised is in a co-ordinate position equivalent to location 3,1 in the output raster, and in a position 2.68, 1.82 in the frame store raster. Point P for example is in co-ordinate position 2,1 in the frame store raster and the remainder (or fractional) values 0.68 and 0.82 are used as interpolation factors for points P, Q, R and S adjacent the point B to be synthesised.
A step in the Y direction from G to H for the start of the next line, is calculated in a similar manner.
This scheme works well when we are dealing with a framestore where the data is stored in a normal fashion and we are creating the rotated image on its output. However, when we wish to build up a rotated image into the framestore then this method of calculating the appropriate addresses and interpolation factors cannot be used and one approach to overcome this problem is to devise a system as shown in FIG. 2. In this arrangement a framestore 10 with associated processor 11 corresponds to the configuration 12 forming the subject of above referenced patent application. In addition, a further framestore 13 is provided so that the rotated output from processor 11 can be presented as an incoming signal to this latter framestore. Thus whilst this system of FIG. 2 meets the requirement of building up a rotated picture into a framestore this adds considerable expense to the system as two frame stores are required to achieve the desired processing function.
An object of the present invention is directed to providing a rotation system capable of processing incoming picture information without relying on a second framestore.